Heat sink

ABSTRACT

A heat sink comprising a conductive plate ( 1 ) to be applied onto the surface to be cooled, the thickness of which gradually increases from the edges ( 4 ) towards a central portion ( 5 ) according to a curvilinear profile ( 6 ) having an upwardly turned concavity, so that an air flow hitting the plate is deflected towards its edges with a substantially horizontal outlet direction. The conductive plate ( 1 ) has preferably arranged thereon a plurality of cooling fins ( 7 ) extending in a substantially radial way from the central portion ( 5 ) to the edges ( 4 ) of the plate.

BACKGROUND OF THE INVENTION

The present invention relates to a heat sink, and in particular to aheat sink which may be used for cooling integrated circuits, laserdevices, electric or other electronic devices.

Heat sinks are known to comprise a plate, generally made of aluminum andprovided on the top with cooling fins or pins, which directly contactsthe housing containing the integrated circuits, in order to increase theheat exchange between the housing and the outside environment, and thusreducing the temperature of the circuit junctions. Since in the lastyears the size and the power of the integrated circuits are increased ingeometric progression, these known heat sinks are no longer capable ofdissipating the heat generated by the new circuits. Therefore, new heatsinks have been designed comprising an axial cooling fan arranged abovethe fins in order to increase the heat exchange between the heat sinkand the surrounding air.

In order to reduce the size of the heat sink and optimize its thermalefficiency, such a cooling fan is arranged straight above the coolingfins, wherefore the air flow generated by the fan perpendicularly hitsthe conductive plate, resulting in turbulence and pressure drops whichgreatly reduce the heat exchange and thus the heat sink efficiency.Furthermore, the central portion of these known heat sinks is moreheated, but the air flow coming from the fan is here reduced. In fact,for space requirements, the fan motor is inserted into the hub of thebladed rotor generating the air flow, so that it tends to outwardly flowwithout affecting the column of air between the rotor hub and the plate.

In order to overcome such drawbacks, a fan could be used with a largerrotor and a more powerful motor, but this solution would result in amore bulky and noisy heat sink, with evident problems when used insidean electronic device.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is thus to provide a heat sink freefrom such drawbacks, i.e. a heat sink which is silent, small-sized andhaving a high heat exchange between the conductive plate and thesurrounding air. Such an object is achieved by a heat sink having themain features specified in claim 1.

Thanks to the special upper profile of the conductive plate of the heatsink according to the present invention, the air flow hitting it in asubstantially perpendicular direction is deflected towards its edgeswith a substantially horizontal outlet direction, resulting in animprovement of the heat sink aerodynamics. Moreover, the greaterthickness at the centre of the conductive plate increases its thermalcapacity and conductivity, so that the greater heat amount at the centreof the integrated circuit is homogeneously conveyed and spreadthroughout the upper surface of the heat sink. The increased thermalcapacity of the conductive plate is also advantageous for allowing theabsorption of possible sudden changes of heat, due to a sudden intensiveuse of the integrated circuit. Finally, since the central portion of theconductive plate is relatively thick, it is possible to provide a cavitywherein a safety thermal sensor may be conveniently housed.

Another advantage of the heat sink according to the present invention isthe fact that the shape and the arrangement of the cooling fins help toimprove the aerodynamics and accordingly the heat exchange of the heatsink. In fact, the conductive plate and the cooling fins form together amember which, by virtue of its structure, similar to a rotor forcentrifiugal pumps, exploits at the best the air flow in order to obtainthe cooling of the heat sink.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Further advantages and features of the heat sink according to thepresent invention will be evident to those skilled in the art from thefollowing detailed description of some embodiments thereof, withreference to the attached drawings, wherein:

FIG. 1 shows a side view of the heat sink according to a first preferredembodiment of the present invention with a sectional view of its righthalf;

FIG. 2 shows a top view of the conductive plate of the heat sink of FIG.1; and

FIG. 3 shows a side view of the heat sink according to a secondembodiment of the present invention with a sectional view of its righthalf.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the heat sink according to a first preferredembodiment of the present invention comprises a plate 1 fastened, e.g.through clamps (not shown in the Figure), on the upper surface of ahousing 2 containing an integrated circuit 3. The thickness of plate 1gradually increases, suitably from edges 4 to a central portion 5, whichis preferably circular and hollow in order to allow the housing of athermal sensor (not shown in the Figure), according to a curvilinearprofile 6 having an upwardly turned concavity. By this arrangement anair flow (indicated by a set of arrows), hitting plate 1 in asubstantially perpendicular direction, is deflected towards edges 4 awith a substantially horizontal outlet direction (indicated as well by aset of arrows). For this purpose, the tangents to such a curvilinearprofile 6 are, in proximity of edges 4 and central portion 5, horizontaland vertical, respectively.

Referring now also to FIG. 2, plate 1 has provided thereon a pluralityof cooling fins 7 extending in a substantially radial way from centralportion 5 to plate edges 4 and being preferably curved with an outwardlyincreasing curvature radius. Junction edge 8 between cooling fins 7 andconductive plate 1, as well as upper leading edge 9 of the fins arepreferably rounded in order to further improve the aerodynamics of theheat sink.

The air flow hitting the heat sink according to the present inventionmay be generated by external fans and conveyed on the conductive platethrough air ducts, or, as in the present embodiment, may be generated byan axial fan 10 of a known type having its rotor, provided with blades11, operated by a motor 12 inserted into a hub 13 of the rotor. Such afan is suitably arranged above plate 1 with its axis perpendicular tothe center of the latter. In order to improve the air flow continuity,the diameter of hub 13 is preferably equal to the diameter of centralportion 5 of plate 1. In another embodiment of the heat sink accordingto the present invention a portion of hub 13 may obviously penetrateinto the cavity of central portion 5 in order to reduce the bulk of theheat sink.

A diffuser joint 14, preferably made of an elastic material forabsorbing the vibrations of motor 12, capable of conveying the air flowcoming from the fan onto the whole upper surface of the plate isarranged between fan 10 and conductive plate 1. By virtue of joint 14,not only the heat sink aerodynamics is improved, but also blades 11 areprevented from being too close to fins 7 and accordingly causing anoxious “siren effect”.

Finally, an air intake 15 is arranged above fan 10, which comprises acentral dome 16 having a diameter substantially equal to the one of hub13 and helping as well to improve the heat sink aerodynamics. An elasticring 17 is inserted between hub 13 and central portion 5 in order toimprove the air flow and absorb the vibrations of motor 12.

In order to manufacture conductive plate 1 of the heat sink according tothe present invention, any known conductive material may be used,suitable for manufacturing heat sinks of a conventional type, such ase.g. aluminum.

In another embodiment, shown in FIG. 3, the lower portion of plate 1 maybe provided with one or more heat anvils 18 for dissipating the heatgenerated by small devices, for instance laser diodes 19, which have anouter surface considerably smaller than the lower surface of plate 1.

Several conductive plates 1 may obviously be used for manufacturing acooling device comprising one or more fans connected through an air ductto said plates.

What is claimed is:
 1. A heat sink, comprising: a conductive plate foraffixation to a coolable surface, the plate including at least one edge,a thickness of the plate gradually increasing according to a curvilinearprofile having an upwardly turned concavity from the at least one edgeto a central circular portion; a plurality of cooling fins affixed toand extending along the plate in a substantially radial manner from thecentral portion to the at least one edge; an axial fan positionedadjacent and above the cooling fins substantially coaxially with thecentral portion, the fan comprising a rotor having a hub ofsubstantially the same diameter as the central portion and a pluralityof blades extending radially from the hub that force air in an axialdirection past a substantial portion of an edge of the fins adjacent tothe blades.
 2. A heat sink according to claim 1, wherein the tangent tosaid curvilinear profile in proximity to the at least one edge of theplate is substantially horizontal.
 3. A heat sink according to claim 1,wherein the tangent to said curvilinear profile in proximity to thecentral portion of the plate is substantially vertical.
 4. A heat sinkaccording to claim 1, wherein the cooling fins are curved.
 5. A heatsink according to claim 4, wherein the curvature radius of the coolingfins increases from the central portion to the at least one edge of theconductive plate.
 6. A heat sink according to claim 1, wherein ajunction edge between the cooling fins and the conductive plate isrounded.
 7. A heat sink according to claim 1, wherein an edge of thefins adjacent to the blades of the axial fan is rounded.
 8. A heat sinkaccording to claim 1, wherein the conductive plate and the cooling finsare made of a single piece.
 9. A heat sink according to claim 1, whereina diffuser joint for conveying the air flow coming from the fan onto theupper surface of the conductive plate is arranged between the fan andthe conductive plate.
 10. A heat sink according to claim 1, furthercomprising an air intake including a central dome having a diametersubstantially equal to the diameter of the rotor hub and positionedabove said fan.
 11. A heat sink according to claim 1, wherein the lowerportion of the conducting plate comprises at least a heat anvil.